Field of the Invention
The present invention relates to a solid-state imaging device having a structure in which a plurality of substrates are stacked.
Description of Related Art
Examples of an autofocus (AF) method include a method of using a phase difference AF sensor, that is, phase difference AF. Considering the conditions of a casing, mounting a phase difference AF sensor in a mirror-less single lens reflex (SLR) camera is more difficult than in a digital SLR camera in the related art. In view of this point, a solid-state imaging device including pixels for acquiring an image and pixels for phase difference AF in an effective pixel area has been provided.
However, since pixels for phase difference AF are present in an effective pixel area of the solid-state imaging device, pixels for acquiring an image are not present at such positions. Thus, the pixels at such positions are handled as defective pixels. In order to secure performance of an AF operation, a predetermined number of pixels for phase difference AF is necessary. For this reason, image data need supplementary defect processing at positions of many pixels for phase difference AF. As a result, it may be difficult to acquire sufficient image quality.
Japanese Unexamined Patent Application, First Publication No. 2013-187475 discloses a solid-state imaging device in which the above-described points are remedied. The solid-state imaging device disclosed in Japanese Unexamined Patent Application, First Publication No. 2013-187475 has a first substrate and a second substrate which are stacked. First photoelectric conversion units for acquiring an image are disposed on the first substrate and second photoelectric conversion units for phase difference AF are disposed on the second substrate.
The solid-state imaging device disclosed in Japanese Unexamined Patent Application, First Publication No. 2013-187475 will be described in detail. FIG. 7 is a constitution of a solid-state imaging device 1000 disclosed in Japanese Unexamined Patent Application, First Publication No. 2013-187475. FIG. 7 shows a cross section of the solid-state imaging device 1000. As shown in FIG. 7, the solid-state imaging device 1000 has a first substrate 80, a second substrate 90, microlenses ML, and color filters CF. The first substrate 80 and the second substrate 90 are stacked.
The color filters CF are disposed on a main surface (the widest surface among a plurality of surfaces forming a surface of the substrate) of the first substrate 80 and the microlenses ML are disposed above the color filters CF. Although there are a plurality of micro lenses ML in FIG. 7, a reference sign of one of the microlenses ML is indicated as a representative thereof. Furthermore, although there are the plurality of color filters CF in FIG. 7, a reference sign of one of the color filters CF is indicated as a representative thereof.
Light from a subject passing through imaging lenses disposed optically forward of the solid-state imaging device 1000 is incident on the micro lenses ML. An image of the light transmitted through imaging lenses is formed through the micro lenses ML. The light with wavelengths corresponding to predetermined colors is transmitted through the color filters CF. For example, red, green, and blue color filters CF are disposed to form a Bayer array with a two-dimensional form.
The first substrate 80 has a first semiconductor layer 800 and a first wiring layer 810. The first semiconductor layer 800 has first photoelectric conversion units 801 configured to convert the incident light into signals.
The first wiring layer 810 has first wirings 811, first vias 812, and a first inter-layer insulating film 813. Although there are a plurality of first wirings 811 in FIG. 7, a reference sign of one of the first wirings 811 is indicated as a representative thereof. Furthermore, although there are a plurality of first vias 812 in FIG. 7, a reference sign of one of the first vias 812 is indicated as a representative thereof.
The first wirings 811 are thin films by which wiring patterns are formed. The first wirings 811 transfer signals generated by the first photoelectric conversion units 801 and other signals (a power supply voltage, a ground voltage, and the like). In an example shown in FIG. 7, four-layer first wirings 811 are formed. The first wirings 811 formed as a fourth layer closest to the second substrate 90 function as light shielding layers 811a. 
Openings 8110 through which only a part of light incident on the first substrate 80 passes are formed between the light shielding layers 811a. The openings 8110 are defined by lateral walls of the light shielding layers 811a. 
The first vias 812 connect the first wirings 811 of different layers. Portions of the first wiring layer 810 other than the first wirings 811 and the first vias 812 are formed of the first inter-layer insulating film 813.
The second substrate 90 has a second semiconductor layer 900 and a second wiring layer 910. The second semiconductor layer 900 has second photoelectric conversion units 901 configured to convert the incident light into signals.
The second wiring layer 910 has second wirings 911, second vias 912, a second inter-layer insulating film 913, and MOS transistors 920. Although there are a plurality of second wirings 911 in FIG. 7, a reference sign of one of the second wirings 911 is indicated as a representative thereof. Furthermore, although there are a plurality of second vias 912 in FIG. 7, a reference sign of one of the second vias 912 is indicated as a representative thereof Although there are a plurality of MOS transistors 920 in FIG. 7, a reference sign of one of the MOS transistors 920 is indicated as a representative thereof.
The second wirings 911 are thin films by which wiring patterns are formed. The second wirings 911 transfer signals generated by the second photoelectric conversion units 901 and other signals (a power supply voltage, a ground voltage, and the like). In the example shown in FIG. 7, two-layer second wirings 911 are formed.
The second vias 912 connect the second wirings 911 of different layers. Portions of the second wiring layer 910 other than the second wirings 911 and the second vias 912 are formed of the second inter-layer insulating film 913.
Each of the MOS transistors 920 has a source region, a drain region, and a gate electrode. The source region and the drain region are diffusion regions formed in the second semiconductor layer 900. The gate electrode is disposed in the second wiring layer 910. The source regions and the drain regions are connected to the second vias 912. The gate electrode is disposed between the source region and the drain region. The MOS transistors 920 process signals transferred through the second wirings 911 and the second vias 912.
The first substrate 80 and the second substrate 90 are electrically connected at an interface between the first substrate 80 and the second substrate 90 via the first vias 812 and the second vias 912.
The solid-state imaging device 1000 shown in FIG. 7 can generate imaging signals from the signals generated by the first photoelectric conversion units 801. Furthermore, the solid-state imaging device 1000 shown in FIG. 7 can generate signals (signals for calculating a phase difference) used for focus detection using phase difference AF from the signals generated by the second photoelectric conversion units 901.